Catalyst-supporting carbon in which catalyst metal particles are supported on conductive supports such as carbon particles has been generally used for an electrode catalyst of a polymer electrolyte fuel cell. Noble metals such as platinum (Pt) and palladium (Pd) are used as the catalyst metal particles. A large amount of noble metal (catalyst) is used, in particular, in direct fuel cells including solid electrolyte membranes because of the low reactivity of liquid fuels. For practical use of fuel cells, not only improvement in fuel cell performance per se but also reduction in amount of the catalyst used, that is, an electrode catalyst with higher activity in a small amount, has been sought.
To reduce the amount of a catalyst used, it is desired that noble metal (catalyst) particles have smaller particle diameters and that the catalyst be formed with particles evenly distributed without forming an aggregate. It has been proposed that a polyalcohol (Non-Patent Document 1) and a surfactant (Non-Patent Document 2) be used as a dispersant for catalyst particles because the control of particle diameters is easy and the resulting catalyst has particles having a small diameter and evenly distributed.
Those conventional dispersants, however, lead to clogging of active sites of the catalyst, and in order to apply them to the electrolyte catalyst of fuel cells, it is necessary to remove those dispersants through chemical reduction (Patent Document 1) or heat treatment (Non-Patent Document 2) after the metal fine particles are supported on a conductive support.